Antioxidants

ABSTRACT

AS ANTIOXIDANT MIXTURE SUITABLE FOR AN AVIATION TURBINE OIL (E.G. AN ESTER OF PENTAERYLTHRITOL) COMPRISES (A) AN ALKYLATED N-PHENYL NAPHTHYLAMINE HAVING AT LEAST ONE ALKYL SUBSTITUENT EACH CONTAINING FROM 3 TO 14 CARBON ATOMS, E.G. N-(TERT-OCTYL PHENYL)-B-NAPHTHYLAMINE AND (B) AN AMINO COMPOUND OF THE FORMULA   1-((CH3-)2-N-),4-((4-((CH3-)2-N-)PHENYL)-CH(-X)-)BENZENE   WHERE X IS HYDROGEN, HYDROCARBYL CONTAINING UP TO 20 CARBON ATOMS, OR THE GROUP   4-((CH3-)2-N-)PHENYL   E.G. N,N&#39;&#39; TETRAMETHYL DIAMINO DIPHENYL METHANE, THE MOLE RATIO OF (A) TO (B) BEING AT LEAST 1*1. THIS ANTIOXIDANT HAS GOOD ANTIOXIDANT POTENCY TOGETHER WITH LOW CORROSIVE TENDENCIES.

United States Patent 3,804,762 ANTIOXIDANTS Graham James Jervis, Abingdon, and Robert Robson, Wantage, England, assignors to Esso Research and Engineering Company No Drawing. Filed Sept. 14, 1972, Ser. No. 289,154 Claims priority, applicati6oz1 G/r7e'i1t Britain, Oct. 6, 1971,

4 Int. Cl. B01j 1/16; C10m 1/34 U.S. Cl. 252-50 9 Claims ABSTRACT OF THE DISCLOSURE As antioxidant mixture suitable for an aviation turbine oil (e.g. an ester of pentaerythritol) comprises (a) an alkylated N-phenyl naphthylamine having at least one alkyl substituent each containing from 3 to 14 carbon atoms, e.g. N-(tert-octyl henyD-B-naphthylamine and (b) an amino compound of the formula CH3 CH3 C IC CH3 where X is hydrogen, hydrocarbyl containing up to 20 carbon atoms, or the group 011, e.g. N,N' tetramethyl diamino diphenyl methane, the mole ratio of (a) to (b) being at least 1:1. This antioxidant has good antioxidant potency together with low corrosive tendencies.

CH3 CH3 on, it orrs where X is hydrogen, hydrocarbyl containing up to 20 carbon atoms, or the group the mole ratio of (a) to (b) being at least 1:1.

Preferred alkylated N-phenyl naphthylamines are monoor di-(C -C alkyl N-phenyl naphthylamines. Thus, one may use isobutyl, hexyl, octyl, decyl, or dodecyl N-phenyl a-naphthylamine or similarly alkylated N-phenyl-fi-naphthylamine; or the dialkyl analogues. The alkyl groups need not of course be the same for the dialkyl compounds. When there is one alkyl substituent on the phenyl group it is preferably in the para position, although it can of course be in the orthoor meta-positions.

When there are two alkyl groups the total number of carbon atoms in the two alkyl groups is preferably not more than 20. There may of course be other substituents in any of the aromatic rings, e.g. halogen atoms, nitro groups, etc. The preferred alkylated N-phenyl naphthyl amine is N-(tert-octyl phenyl)- 8-naphthylamine.

Although preferably it is the phenyl group which is alkylated, one or both of the aromatic rings of the naphthylamine part of the molecule may be alkylated, and the term fal-kylated N-phenyl naphthylamine covers both possibilities. Suitable alkyl group substituents of the naphthylamine part of the molecule include those specifically mentioned above.

To avoid corrosion problems it is preferred that Component '(a) should contain no sulphur atoms present as a substituent or part of a substituent group.

The preferred Component (b) is N,N' tetra methyl diamino diphenyl methane, i.e. when X is hydrogen. It could however be for example 1,1-bis(N,N dimethyl amino phenyl) heptane, N,N tetra methyl diamino triphenyl methane or N,N',N hexa methyl triamino triphenyl methane. When X is hydrocarbyl, it preferably contains from 2 to 12 carbon atoms.

The mole ratio of (a) to (b) must be at least 1:1, and is preferably between 1:1 and 13:1, especially between 1:1 and 10:1. A particularly preferred mole ratio is between 2:1 and 4:1 e.g. about 23:1.

The antioxidant mixture of the invention is suitable for use in a lubricating oil, especially an aviation turbine oil. When added to a lubricating oil, it should be added in minor proportion, preferably 0.001 to 10.0% by weight, e.g. 0.1 to 5.0% by weight, based on the weight of lubricating oil.

The lubricating oil to which the antioxidant mixture may be added can be any mineral, animal, fish, vegetable or synthetic oil, for example, petroleum oil fractions ranging from spindle oil to SAE 30, 40 or 50 lubricating oil grades, castor oil, animal or fish oils or oxidized mineral oil, e.g. palm oil, lard oil, tallow oil, arachis oil or sperm oil.

The preferred lubricating oil is a synthetic ester and suitable diesters include diesters of the general formula ROOCR'COOR and RCOOR'OOCR where R represents a C to C alkyl group, while R represents a C to C saturated aliphatic hydrocarbon group or an ether-interrupted saturated aliphatic hydrocarbon group. The above types of esters may be prepared from alcohols and dicarboxylic acids or glycols and monocarboxylic acids.

Another suitable class of ester lubricant are the polyesters which are prepared by reacting polyhydric alcohols e.g. those having 2 to 12 hydroxyl groups per molecule and 2 to 40 carbon atoms per molecule, such as trimethylolpropane, pentaerythritol' and di-pentaerythritol with monoand/or di-carboxylic acids such as butyric acid, caproic acid, caprylic acid and pelargonic acid, or adipic, sebacic or azelaic acids.

The complex esters which may be used as base oils are formed by esterification reactions between a dicarboxylic acid, a glycol and an alcohol and/or a monocarboxylic acid. These esters may be represented by the following formulae:

wherein R represents alkyl radicals derived from a monohydric alcohol, R represents hydrocarbon radicals derived from a dicarboxylic acid, e.g. alkanedioic acids, R represents divalent hydrocarbon or hydrocarbon-oxy radicals such as -CH (CH or or CH CH(CH )(OCH CH(CH derived from an alkylene glycol or polyalkyleneglycol, while R represents the alkyl group derived from a monocarboxylic acid.

n in the complex ester molecule which is an integer will usually range from 1 to 6 depending upon the product viscosity desired which is controlled by the relative molar ratio of the glycol or polyglycol to the dicarboxylic acid. In preparing the complex ester, there will always be some simple ester formed, i.e. n=0, but this will generally be a minor portion. In general these complex esters will have a total of between 15 and 80, e.g. between 20 and 65 carbon atoms per molecule.

Particularly suitable lubricants are esters of polyhydric alcohols having the formulae where R is a CH OH group or an alkyl group, e.g. an alkyl group containing 1 to 6 carbon atoms. Thus, suitable esters of this type are the neopentyl polyol esters of trimethylol ethane, trimethylol propane, trimethylol butane and of pentaerythritol or di-pentaerythritol.

The preferred acids used to esterify trimethylol proprone are the C to C monocarboxylic acids. Particularly preferred at the C -C esters, e.g. C (caprylic) and C (pelargonic) acid esters. Mixtures of these C -C acids may be used. When such an acid mixture is used, it is preferred that the mixture average between C and C Although more difiicult to form, it is even more preferred that one methylol group be esterified with a neoheptanoic acid, e.g. 2,2-dimethylpentanoic acid, and the remaining methylol groups esterified with non-hindered acids, e.g. pelargonic acid. This particular ester is substantially as thermally stable as the completely hindered ester but has superior volatility and low temperature characteristics.

The preferred acids used to esterify pentaerythritol are the C C monocarboxylic acids with the more preferred esters being those of C to C acids, e.g. n-valeric, isovaleric, 2-ethyl butyric, caproic, n-heptylic, n-octanoic or 2-ethyl hexoic acids or a mixture of C to C acids.

Blends of diesters with minor proportions of one or more thickening agents may also be used as lubricants. Thus one may use blends containing up to 50% by volume of one or more water insoluble polyoxyalkylene glycols, for example, polyethylene or polypropylene glycol, or mixed oxyethylene/oxypropylene glycol.

Formulations suitable for gas turbine lubrication include from 65 to 90 vol. percent of one or more diesters of azelaic or sebacic acid and a C -C branched chain alcohol, particularly of 2-ethyl hexanol, or 0x0 alcohols consisting predominantly of C C 01- C alcohols, or of mixtures of such alcohols, and 35 to 10% of polywherein R R and R are hydrogen or (I -C alkyl groups and wherein not more than two such groups is hydrogen, and n is an integer greater than 1. Particularly useful compounds are poly-oxypropylene glycol monoethers and the corresponding diethe-rs.

The thermal stability of such diester/polyoxyalkylene glycol ethers may be improved if a small proportion of a complex ester derived from three or more carboxylic acids or alcohols, at least two of which are difunctional acids or alcohols is incorporated. Such complex esters may 'be glycolor dicarboxylic acid centered, the molecule being terminated with a mono-hydroxy or monocarboxylic acid compound. A particularly preferred complex ester of this type is derived from polyethylene glycol of molecular weight 200, 2 molecules of sebacic or azelaic acid, and 2 molecules of a (J -C branched chain aliphatic monohydric alcohol, particularly 2-ethyl hexanol.

Other additives which may be incorporated in the lubricating oil include corrosion inhibitors, e.g. sebacic acid, a metal deactivator such as quinizarin, a foam inhibitor, e.g. a silicone polymer such as dimethyi silicone, or an antiwear additive, e.g. neutral alkyl phosphates such as tricresyl phosphate, neutral alkyl aryl phosphates, or neutral phosphonates.

EXAMPLE 1 Various antioxidant mixtures were prepared by blending together N-(tert-octyl henyD-fi-naphthylamine (abbreviated C -PBNA) and N,N'-tetra methyl di-amino diphenyl methane (abbreviated TMDDPM).

Each mixture was separately added to a synthetic ester base oil which also contained 1.0% by weight of tricresyl phosphate. The base oil was a mixture of complete esters obtained by esterification of 90% pentaerythritol and 10% dipentaerythritol with a mixture of (C -C fatty acids.

The blends of oil plus antioxidant were subjected to the Rolls-Royce Oxidation Test (R-R1001) and the results obtained given in the table below. For comparison purposes tests were carried out using C -PBNA alone and TMDDPM alone, and a blend where the mole ratio of C -PBNA to TMDDPM is less than 1:1 i.e. 0.77:1.

In Tests (1) and (2) which relate to antioxidants not within the scope of the invention, there were vapour phase deposits as a varnish in the test tube, thus indicating that these two antioxidants would be too dirty to be acceptable.

In Tests (5) and (6) which also relate to antioxidants not within the scope of the invention it is noted that TABLE Rolls Royce test (temp., 215 C., 72 hours duration) Antioxidant and percent based on Induc- Benzene weight of oil Mole Percent tion A kv. insolratio volaperiod 210 F., ubles, Test (a) (b) (a) (b) tility (hrs.) percent A ten percent 1 (1) 1% TMDDPM 37. 5 0 (2) 1.0%Cs-PBNA" 1% TMDDPM 0. 77:1 28. 4 2A 125 4. 0. 03 (3) 1.5% Ca-PBNA 0.5% TMDDPM 2.31:1 23.4 36 96 5.59 0.03 (4) 2% Cg-PB NA 31. 6 24 149 4. 5 0. 01

Temp. 215 0., duration increased to 192 hrs.

( 2% Cs-PBNA 56. 6 24 (Solidified after 168 hrs.) (6) 3% CE'PBNA 54. 7 48 428 4. 32 0. 03 (7)" 3.0% Ca-PBNA 1.0% TMDDPM 2. 31:1 28. 9 -192 64 2. 50 0. 04 (8) 3 o Cs-PBNA 0 TMDDPM 3. 07:1 34. 7 84 131 4. 34 0. 04 3. 0% PM 3. 84:1 37. 1 82 142 4. 22 0. 03 3.0% Ca-PBNA 0.50% TMDDPM 4. 61:1 40. 0 89 118 3.75 0. 02

l Maximum acceptable value 0.05% by weight.

oxyalkylene glycol ether represented by the general formula:

Lei.

'1 D. Eng a. D. 2497 Supplement Method No. 12.

EXAMPLE 2 An antioxidant mixture of TMDDPM and C -PBNA was prepared and added to a synthetic ester mixture consisting of complete esters prepared from mixed C to C fatty acids and a mixture of 80 wt. percent pentaerythritol, 10 wt. percent dipentaerythritol and 10 wt. percent trimethylol propane. The ester mixture contained 1 wt. percent of tricresyl phosphate and the antioxidant components were present in the synthetic ester as 1% TMDDPM and 3.0% C -PBNA by weight based on weight of ester (mole ratio of (a):(b)=2.3:1).

For comparison purposes, the procedure was repeated exactly except that instead of using TMDDPM the ester mixture contained 1.0 wt. percent of N,N'-tetraethy1 diamino diphenyl methane (abbreviated TEDDPM) (mole ratio (a):(b)=2.8:1).

When subjected to the Rolls-Royce Oxidation Test at 215 C. over 192 hours the following results were obtained.

Induction period (hrs.)

Benzene insolubles, percent A kv. 210 F., percent Percent vola- Anttoxidant tility A ten 1.0 wt. percent 'IMD PM, 3.0 wt. percent C PBNA 1.0 wt. per cent TEDDPM, 3.0 wt. parcent Ca- EXAMPLE 3 An antioxidant mixture of TMDDPM and N-(n-heptyl phenyl)- 9 naphthylamine (abbreviated Cq-PBNA) was prepared and added to a synthetic ester mixture consisting of complete esters prepared from mixed C -C fatty acids and a mixture of 90 wt. percent pentaerythritol and 10% di-pentaerythritol. The ester mixture contained 1 wt. percent of tricresyl phosphate and the antioxidant components were present in the synthetic ester as 1.0% TMDDPM and 3.0% Cq-PBNA, by weight based on weight of ester (mole ratio (a) :(b)=2.4:1).

Another antioxidant mixture was prepared in the same way so that the synthetic ester contained 1.0 wt. percent N,N',N" hexamethyl triamine triphenyl methane (HMTATPM) and 3.0 wt. percent Cg-PBNA (mole ratio (a):(b)=3.14:1).

When subjected to the Rolls-Royce Oxidation Test at 215 C. over 192 hours the following results were obtained:

Benzene insolubles, percent A kv. 210 F.,

tllity,

percent percent period (hrs.) A ten It can be seen that good results are achieved with both antioxidants within the scope of the invention.

What is claimed is:

1. An antioxidant mixture comprising (a) an alkylated N-phenyl naphthylamine having from one to two alkyl substituents each containing from 3 to 14 carbon atoms, and (b) an amino compound of the formula where X is hydrogen, hydrocarbyl containing up to 20 carbon atoms, or the group the mole ratio of (a) to (b) being within the range of 1:1 to 13:1.

2. A mixture according to claim 1 wherein component (a) has two alkyl groups and the total number of carbon atoms in the two alkyl groups is not more than 20.

3. A mixture according to claim 1 wherein component (a) is N-(tert-octyl phenyl)- 8-naphthylamine.

4. A mixture according to claim 1 wherein the mole ratio is between 2:1 and 4:1.

5. A mixture according to claim 1 wherein component (b) is N,N' tetramethyl diamino diphenyl methane.

6. A lubricating oil composition comprising a major proportion by weight of a lubricating oil and a minor proportion by weight of the antioxidant mixture according to claim 1.

7. A lubricating oil composition according to claim 6 wherein the lubricating oil is a synthetic ester oil.

8. A mixture according to claim 1 wherein component (a) is N- (heptyl henyD-fl-naphthylamine.

9. A mixture according to claim 1 wherein component (b) is N,N,N" hexamethyl triamino triphenyl methane.

References Cited UNITED STATES PATENTS 2,097,162 10/1937 Musselman et a1. 25250 2,270,577 1/ 1942 Bergstrom et al. 252401 2,294,726 9/1942 Dreshfield 252401 3,011,976 12/1961 Uyba et 'al. 252-50 3,121,691 2/ 1964 Eickenmeyer 252-50 3,210,281 10/ 1965 Peeler 252-50 3,660,290 5/1972 Schlobohm 252-401 3,696,851 10/ 1972 Randell 252--50 DANIEL E. WYMAN, Primary Examiner A. P. DEMERS, Assistant Examiner US. Cl. X.R. 252-401 

